In recent years, a fixing device of an image forming apparatus includes a heater divided from a heating section. Such an image forming apparatus can enable the heating section to selectively generate heat in response to a size of a sheet, and can suppress power consumption at the time of heating the sheet. However, in order to control the heating section, it is necessary to measure a temperature of each heating section, or a plurality of temperature detection elements corresponding to the quantity of the heating sections is necessary.